The present invention relates to a carbon fiber thread having high performance and particularly to a carbon fiber thread which exhibits excellent processability, shape retention, and reinforcing effect, for example, when used for stitching of a reinforcing fabric for a composite material.
A woven fabric, such as a carbon fiber woven fabric or a hybrid woven fabric comprising a carbon fiber and other fiber having high strength and high modulus, is utilized as a reinforcing material for a composite material. When such a fabric is used as a reinforcing material, it is formed after, for example, it is either impregnated with a matrix resin and plural impregnated fabrics are laminated or preformed into a desired shape and impregnated with a matrix resin. When either a plurality of fabrics are laminated, or a fabric preformed into a desired shape is impregnated with a matrix resin, or hot forming is conducted, the above-described laminated fabrics are generally stitched with a stitching thread in order to improve the shape retention or the peel strength between the laminated fabrics.
Examples of the stitching thread include a glass fiber, a polyester fiber, an aramid fiber, and a blended yarn of carbon fiber and organic fiber. However, these stitching threads have drawbacks, such as high water absorption, poor heat resistance, poor adhesion to a matrix material such as resin or poor strength and modulus, which make it impossible to sufficiently reflect the characteristics of the reinforcing fabric in the composite material.
On the other hand, the above-described problems may be solved by preparing the stitching thread of a carbon fiber only. However, the carbon fiber has characteristics such that it is strong against tension but fragile against bending. This raised problems such as occurrence of breakage and fuzzing of the thread caused by thrust with a needle and friction with the fabric in the process of stitching. Therefore, it is the state of the art that no satisfactory stitching thread for reinforcing fabric has been prepared.